This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.
|Medical Terms||Other Names||
|80%-99% of people have these symptoms|
|Abnormality of metabolism/homeostasis||
Metabolism abnormality[ more ]
|Global developmental delay||0001263|
Mental retardation, nonspecific
Mental-retardation[ more ]
Low or weak muscle tone
|30%-79% of people have these symptoms|
Psychiatric disturbances[ more ]
|Bilateral tonic-clonic seizure||
Grand mal seizures
|Generalized myoclonic seizure||0002123|
Repeated seizures without recovery between them
|1%-4% of people have these symptoms|
Degeneration of cerebellum
Symptoms begin in childhood
|Delayed speech and language development||
Deficiency of speech development
Delayed language development
Delayed speech acquisition
Delayed speech development
Impaired speech and language development
Impaired speech development
Language development deficit
Late-onset speech development
Poor language development
Speech and language delay
Speech and language difficulties
Speech delay[ more ]
Decreased muscle tone
Low muscle tone[ more ]
Decreased reflex response
Decreased reflexes[ more ]
Onset in first year of life
Onset in infancy[ more ]
Signs and symptoms begin before 15 years of age
|Young adult onset||0011462|
|Percent of people who have these symptoms is not available through HPO|
|Abnormality of eye movement||
Abnormal eye movement
Abnormal eye movements
Eye movement abnormalities
Eye movement issue[ more ]
Aggressiveness[ more ]
Excessive, persistent worry and fear
|Decreased succinic semialdehyde dehydrogenase level||0032530|
|Elevated circulating gamma-aminobutyric acid concentration||0032529|
|Elevated CSF 4-hydroxybutyric acid concentration||0032532|
|Elevated CSF gamma-aminobutyric acid concentration||0032531|
|Elevated urinary 4-hydroxybutyric acid||0032528|
|Generalized non-motor (absence) seizure||
Brief seizures with staring spells
Sensory hallucination[ more ]
More active than typical
|Increased level of gamma-aminobutyric acid in urine||0500253|
If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.
If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.
You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.
Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.
Conditions with similar signs and symptoms from Orphanet
The main differential diagnoses include gamma-aminobutyric acid transaminase deficiency and homocarnosinosis (see these terms).
Visit the Orphanet disease page for more information.
Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.
Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.
These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.
Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question
How soon after birth can this be diagnosed? When is it known how severely an individual is affected? Is it possible to live a normal life? See answer